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Regulatory Assets and Liabilities (ROE of New Mexico Gas Company) (Details) $ in Millions, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 CAD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 CAD ($)
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory Liabilities | $ 2,610 |  | $ 2,468
New Mexico Gas Company [Member] |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Public Utilities, Approved Return on Equity, Percentage | 10.00% |  |
Public Utilities, Approved Equity Capital Structure, Percentage | 52.00% |  |
Regulatory Liabilities |  | $ 8 |

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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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